The invention relates to the operation of hollowing out the pulp canals of teeth, utilizing endodontistry instruments of the type consisting in a boring bit fitted to a vibrating handgrip; such a grip may be of a type capable of transmitting sonic or ultrasonic vibratory motion to the bit fitted, or may be purely mechanical, but at all events, will be designed to vibrate the bit rather than investing it purely with rotary motion in conventional manner.
With vibration thus transmitted from the grip to the bit in combination with suitable fluids supplied either previously or simultaneously to the cavity of the tooth, the pulp is dissolved, and a microscopic break-up in the dentine of the canal wall is brought about; in this way, the pulp canal is hollowed out in readiness for filling.
With the advent of vibrating instruments, it has become clear that conventional drilling bits are not able to exploit vibratory motion to full advantage.
In effect, conventional instruments utilize a type of bit exhibiting a shape and a cutting surface best suited to vertical filing and/or rotary action, whether manually or mechanically induced, which are movements that hitherto have typified the method of removing pulp from a tooth to be filled. FIG. 1 of the accompanying drawings shows the schematic representation of a conventional bit; this is flanked by a tabulated summary of the principal specifications and standard diameters currently in use, which are to ISO. In the table, D1, D2 and D3 denote the diameter, in mm, of each corresponding section of the bit, the working tine portion PO of which measures 16 mm from end to end. In the same table, "N. norm" denotes a standard reference number for the relative conventional bit, which reflects the tip diameter D1 expressed in 100ths of one mm.
With the introduction of vibrating endodontistry instruments, it has been observed that the vibratory motion transmitted by the grip is more pronounced in the more flexible part of the tine, in other words, the part that fans out when in operation to assume the shape of a cone (see FIG. 2), the base of which coincides with its tip.
The base diameter of the vibrating cone shape in question can be adjusted, by way of a special device incorporated into the grip, to give an oscillatory excursion of between 1 and 1.5 mm. Thus it happens that the base diameter of the cone can blanket any tip diameter across the entire range of conventional bits (see table, FIG. 1), and as a result, one of the essential features of these bits, namely, the fact of their increasing in tip diameter from one size to the next, is set at nothing.
The use of a set of conventional vibrating bits, increasing them progressively in size to the end of enlarging the cavity, is accompanied by a similarly progressive increase in the risk of the pulp canal becoming ovalized, of laceration, and of drift from the position of the apical extremities, which are impossible to assess exactly beforehand in vivo. by the same token, the passage from one size of bit to the next dictates an increase in rigidity of the tine, and with it, the impossibility of successfully following the curvilinear anatomy of the canal.
Finally, the vibratory motion which projects the bit sideways against the dentine wall of the pulp canal gives rise to the need for abrading surfaces different from those designed for the manually or mechanically induced linear or rotary movement of conventional instruments.
Accordingly, the object of the invention is to overcome the limitations and eliminate the drawbacks mentioned above, by setting forth a set of specially designed bits for endodontistry instruments, which are able to exploit the operating characteristics of a vibrating grip to the full.